The present invention relates generally to apparatus and methods for irradiating targets with radio-frequency (RF) or microwave radiation, and more specially to systems for controlled application of radiation to biological tissues.
Although the conventional treatment such as surgery, x-ray radiation, and chemotherapy have been successful in treating cancers, they are frequently ineffective against many types of cancers and often have severe adverse side effects at the necessary treatment levels. In contrast, RF/microwave hyperthermia appears to have the potential for being extremely effective in the treatment of many or most types of human cancers without the above mentioned side effects.
It is reported that RF/microwave hyperthermia, both alone and in combination with other treatment methods, provides evidence of effectiveness. Medical researches further show that most types of human cancers can be thermally destroyed with heating up to the temperature range of 42xc2x0 C.xcx9c45xc2x0 C. Moreover, many types of cancerous tissues have been reported to have substantially poorer than normal heat transfer or dissipation characteristics due to reduced blood flow and decreased nutrition. Consequently, such types of cancers appear capable of preferential hyperthermia treatment.
Another well-known advantage of RF/microwave hyperthermia is that the RF/microwave energy may be controlled to form a focussed energy pattern inside the tumor tissues by controlling the power level and phase of each applicator, as well as by the arrangement of the applicator array. Thus it is possible to create a selected heating to kill cancers rather than damaging the normal cells through the above-described double selection feature of RF/microwave hyperthermia.
In the past years, various RF/microwave hyperthermia systems have been proposed, which are suitable for either invasive or noninvasive therapy, either for sub-surface tissue or a deep region, either small or large tumors. Among these systems, the radiation applicator is the key component, which may have variants such as monopole, dipole, needle-type, two-plates, waveguide end, horn, planar patch etc. Different applicators have their own preference for different hyperthermia system and suitable for different location of therapy, mainly because of the different penetration capability.
A powerful hyperthermia system should have the following basic criteria:
The penetration depth is large enough to make the deep target be heated effectively, meanwhile not to damage the bypass and surrounding normal tissues.
Temperature distribution within the tumor volume should be well defined and uniform, while the fall-off of temperature beyond the tumor volume should be steep.
The focusing energy pattern can be tunable with a good resolution in order to treat different location and to vary the heating pattern for avoiding hot spots occurrence.
A good trade-off between penetration and selection should be achieved.
A good trade-off between uniformity and selection should be achieved.
In addition, the level of hyperthermia should be precisely controllable, which may be through the feedback of accurate temperature and physiological monitoring.
It is better to combine with other treatment methods in order to improve overall therapy effectiveness.
To review the existing hyperthermia devices, it is noted that most of them have not satisfied the above requirements completely, or need some improvement.
Noninvasive RF/microwave hyperthermia system employs the phase-amplitude controlled external RF/microwave radiation array, which is suitable for heating large deep target. But it suffers from the limited depth of penetration, the development of standing waves to create hot spots, and poor resolution not to make it really shift the energy peak. These shortcomings limit their applications to the small deep tumors, which most often face in practical clinical cases.
On the other hand, most existing invasive devices with a single applicator lack beam steering and uniformity of electromagnetic (EM) field.
Overall difficulties include that both invasive and noninvasive hyperthermia treatment systems have not integrated as a single device which can make the therapy more flexible and much easier to adjust the heating pattern for different depth of targets. Furthermore, even among other proposed invasive array focusing systems, the boundary of heating pattern by existing hyperthermia devices are not well defined, thus it does not realize a truly selected hyperthermia.
One typical example of noninvasive hyperthermia is Turner""s invention, U.S. Pat. No. 4,586,516, in which all the dipole applicators are placed outside of the patient body thus its application is suitable for the deep large volume of tumors. For an example of invasive hyperthermia, in U.S. Pat. No. 4,448,198, after inserting into the body by aid of a medical catheter, every coaxial monopole antenna acts as radiating applicator to obtain coherent overlap of RF/microwave energy, and only allow parallel applicators in one direction in order to achieve
Some other invasive devices such as U.S. Pat. No. 5,536,267, 5,855,576, and 5,951,547 employ multiple deflected needle-type electrodes to induce high frequency current through the ablation volume. These divergently deflected arrays of electrodes are used mainly for increasing radiation area. However they still lack well-defined radiation and thermal boundary.
For the microwave acupuncture application of U.S. Pat. No. 4,621,642, Chen""s invention utilizes a solid or grand horn for shielding radiation back into the environment and improving the impedance matching between body and antenna. But it can not be inserted into body hence not to make microwave radiation inside the body be bounded.
Typically, the RF/microwave hyperthermia utilizes frequency band from 100 MHz to 3000 MHz. Hence significant amounts of RF/microwave energy are absorbed by surface or epidermis layers because of their high loss properties. The amount or the depth of penetration, which causes effective heating, is dependent upon the frequency of radiation. For example, the depth of penetration in the human muscle is only 3 cm at 915 MHz; while at 100 MHz, still only around 6.5 cm of penetration. It means that it is not a good way to radiate RF/microwaves from the exterior of the body to approach the deep tissues. So it is better to use, for example, a small coaxial cable antenna to deliver RF/microwave energy directly to the target that it needs to heat in the deepest location. Such a direct energy delivery scheme is very suitable for treating small deepest tumors, which is the most common case in the realistic clinical applications.
However, it is obvious that the frequency also determines the size of the radiation volume. The lower frequency is chosen, the larger size of the radiation volume must be produced, and vice versa.
In order to improve focus capability, the frequency should be chosen higher, but may cause not to heat effectively along the edge areas of the target tumor tissues because of the rapid power attenuation from the central of the inserted antenna. It means a good heating uniformity within the target is not achievable. When the frequency is set too low, the RF/microwaves may propagate or scatter into the surrounded normal tissues. This means the selection of heating is not acceptable.
The trade-off between good uniformity and good selection of heating must determine an optimized frequency of exact value. In an actual application, this is very difficult job, because the human body is such a complicated EM media, and may vary with case by case. However, lowering down the operating frequency should enlarge the radiation volume thus improve the heating uniformity inside the tumor volume; while as in the present invention, introducing a set of grounded needles locating along the tumor boundary to protect the surrounded normal tissues from radiation can improve the heating selection.
Therefore, one of the main objectives for this invention is to develop an RF/microwave hyperthermia apparatus having the basic advantages of the existing devices in the art and improving their performances and functionality.
According to the present invention, a novel apparatus comprises of a single applicator or an array of applicators excited by the RF/microwave sources and connecting with some kind of controlling and monitoring subsystems. It is used for either hyperthermia or acupuncture to provide invasive and noninvasive medical treatment to the target inside a human body.
The individual applicator consists of a central signal coaxial needle surrounded by a plurality of grounded needles to enclose the heated target. The advantages of such a configuration of the applicator are to guide the wave to move forwardly further resulting in a penetration improvement, and also to reduce the backward reflection from the radiator end, thus to make the boundary of heating pattern clear-defined.
Such a guided-wave needles array producing a quasi-TEM electromagnetic radiation makes even one individual radiation applicator have a capability of EM energy focus. The central part of the applicator forms a coaxial cable type antenna to deliver RF/microwave energy directly into the target site. It also has a tunable feature to vary the position of each needle and the resonance length of the coaxial needle radiator to make individual applicator create a variable thermal pattern.
In addition, the frequency, amplitude, and relative phase from each applicator of the formed array system can be varied by the RF/microwave generator, amplifier, and phase shifter to create optimized heating patterns via the feedback of a real time temperature profile and image display through a computer control.
The grounded needles are preferably hollow, not limited to solid. This presents two advantages, at least: one is to make it have ability to introduce a variety of therapeutic infusion mediums through the hollow grounded needles and the central hollow coaxial cable; on the other hand, make it easy to mount some temperature sensors inside the hollow. Thus it can provide three-dimensional infusion and three-dimensional temperature measurement.
Several different combination of applicator arrays or individual are suitable for use with the system to provide effective treatment to different location of the tumors or any other diseased tissues, for example, subsurface or deep, small or large, central or eccentric hyperthermia regions or acupuncture points. The invented system has integrated invasive and noninvasive hyperthermia to cancers, and invasive and noninvasive acupuncture to acupuncture points as a single device, which performs flexible and multiple functions.
The main advantages and unique features of the present invention compared with the existing devices are: using grounded needles and inserting into the body to bound or shield energy and to well define the heating boundary thus to protect the surrounded normal tissues from radiation and heating, and tuning both the radiator length and the insertion depth of the inner coaxial-cable antenna and the grounded needles to make it adjustable for different size and different depth of target tumor tissues hence varying the thermal patterns, therefore realizing a really selected and localized heating therapy.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are presented by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.